fix(plugins): diagnostics crash minimales pour l'install de plugin (backend)

Écran noir hello-plugin (#120) récidivant après 3 fixes déjà mergés sans
capturer la cause réelle : on ne pouvait pas savoir si le crash venait de
l'install, du reconcile MCP ou d'un panic silencieux. Ajoute un panic hook
qui logge thread/location/backtrace, trace les étapes install/reconcile/
asset-protocol dans idea.log, et remplace les `.expect()` du superviseur MCP
plugin par une erreur typée au lieu d'un panic sur mutex empoisonné.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

crates/app-tauri/src/plugins.rs

@@ -57,12 +57,28 @@ pub async fn plugin_install_from_archive(
     path: String,
     state: State<'_, AppState>,
 ) -> Result<PluginInstallResultDto, ErrorDto> {
-    state
+    application::diag!("[plugins] install archive start path={path}");
+    let result = state
         .install_plugin_from_archive
         .execute(path)
         .await
         .map(PluginInstallResultDto::from)
-        .map_err(ErrorDto::from)
+        .map_err(ErrorDto::from);
+    match &result {
+        Ok(result) => application::diag!(
+            "[plugins] install archive ok plugin={} version={} hash={} lifecycle={:?}",
+            result.plugin.id,
+            result.plugin.version,
+            result.review.content_hash,
+            result.plugin.lifecycle_state
+        ),
+        Err(err) => application::diag!(
+            "[plugins] install archive failed code={} message={}",
+            err.code,
+            err.message
+        ),
+    }
+    result
 }
 
 /// Installs a plugin from a local directory snapshot.
@@ -71,12 +87,28 @@ pub async fn plugin_install_from_directory(
     path: String,
     state: State<'_, AppState>,
 ) -> Result<PluginInstallResultDto, ErrorDto> {
-    state
+    application::diag!("[plugins] install directory start path={path}");
+    let result = state
         .install_plugin_from_directory
         .execute(path)
         .await
         .map(PluginInstallResultDto::from)
-        .map_err(ErrorDto::from)
+        .map_err(ErrorDto::from);
+    match &result {
+        Ok(result) => application::diag!(
+            "[plugins] install directory ok plugin={} version={} hash={} lifecycle={:?}",
+            result.plugin.id,
+            result.plugin.version,
+            result.review.content_hash,
+            result.plugin.lifecycle_state
+        ),
+        Err(err) => application::diag!(
+            "[plugins] install directory failed code={} message={}",
+            err.code,
+            err.message
+        ),
+    }
+    result
 }
 
 /// Enables or disables a plugin.
@@ -145,13 +177,30 @@ pub fn plugin_asset_protocol(
     app: &AppHandle,
     request: http::Request<Vec<u8>>,
 ) -> Response<Vec<u8>> {
+    let uri = request.uri().to_string();
     match plugin_asset_response(app, request) {
-        Ok(response) => response,
-        Err((status, message)) => Response::builder()
-            .status(status)
-            .header(header::CONTENT_TYPE, "text/plain; charset=utf-8")
-            .body(message.into_bytes())
-            .expect("valid protocol error response"),
+        Ok(response) => {
+            application::diag!(
+                "[plugins] asset ok uri={} status={} bytes={}",
+                uri,
+                response.status(),
+                response.body().len()
+            );
+            response
+        }
+        Err((status, message)) => {
+            application::diag!(
+                "[plugins] asset failed uri={uri} status={status} message={message}"
+            );
+            Response::builder()
+                .status(status)
+                .header(header::CONTENT_TYPE, "text/plain; charset=utf-8")
+                .body(message.into_bytes())
+                .unwrap_or_else(|e| {
+                    application::diag!("[plugins] asset error response build failed: {e}");
+                    Response::new(Vec::new())
+                })
+        }
     }
 }